make assoc fn inherit const stability from inherent const impl blocks

Currently, one cannot add any const stability annotations on the
individual assoc fns at all, as the specific pass that checks for const
stability on const fn seems to run as a HIR visitor. I suspect there are
things to be cleaned up there.

Author: fee1-dead

compiler/rustc_passes/src/stability.rs

@@ -54,7 +54,7 @@ fn inherit_const_stability(tcx: TyCtxt<'_>, def_id: LocalDefId) -> bool {
     match def_kind {
         DefKind::AssocFn | DefKind::AssocTy | DefKind::AssocConst => {
             match tcx.def_kind(tcx.local_parent(def_id)) {
-                DefKind::Impl { of_trait: true } => true,
+                DefKind::Impl { .. } => true,
                 _ => false,
             }
         }

library/alloc/src/raw_vec/mod.rs

@@ -165,12 +165,12 @@ const fn min_non_zero_cap(size: usize) -> usize {
     }
 }
 
+#[rustc_const_unstable(feature = "const_heap", issue = "79597")]
 const impl<T, A: [const] Allocator + [const] Destruct> RawVec<T, A> {
     /// Like `with_capacity`, but parameterized over the choice of
     /// allocator for the returned `RawVec`.
     #[cfg(not(no_global_oom_handling))]
     #[inline]
-    #[rustc_const_unstable(feature = "const_heap", issue = "79597")]
     pub(crate) fn with_capacity_in(capacity: usize, alloc: A) -> Self
     {
         Self {
@@ -183,7 +183,6 @@ const impl<T, A: [const] Allocator + [const] Destruct> RawVec<T, A> {
     /// caller to ensure `len == self.capacity()`.
     #[cfg(not(no_global_oom_handling))]
     #[inline(never)]
-    #[rustc_const_unstable(feature = "const_heap", issue = "79597")]
     pub(crate) fn grow_one(&mut self)
     {
         // SAFETY: All calls on self.inner pass T::LAYOUT as the elem_layout
@@ -411,10 +410,10 @@ unsafe impl<#[may_dangle] T, A: Allocator> Drop for RawVec<T, A> {
     }
 }
 
+#[rustc_const_unstable(feature = "const_heap", issue = "79597")]
 const impl<A: [const] Allocator + [const] Destruct> RawVecInner<A> {
     #[cfg(not(no_global_oom_handling))]
     #[inline]
-    #[rustc_const_unstable(feature = "const_heap", issue = "79597")]
     fn with_capacity_in(capacity: usize, alloc: A, elem_layout: Layout) -> Self
     {
         match Self::try_allocate_in(capacity, AllocInit::Uninitialized, alloc, elem_layout) {
@@ -428,7 +427,6 @@ const impl<A: [const] Allocator + [const] Destruct> RawVecInner<A> {
             Err(err) => handle_error(err),
         }
     }
-    #[rustc_const_unstable(feature = "const_heap", issue = "79597")]
     fn try_allocate_in(
         capacity: usize,
         init: AllocInit,
@@ -474,7 +472,6 @@ const impl<A: [const] Allocator + [const] Destruct> RawVecInner<A> {
     /// - `elem_layout`'s size must be a multiple of its alignment
     #[cfg(not(no_global_oom_handling))]
     #[inline]
-    #[rustc_const_unstable(feature = "const_heap", issue = "79597")]
     unsafe fn grow_one(&mut self, elem_layout: Layout)
     {
         // SAFETY: Precondition passed to caller
@@ -489,7 +486,6 @@ const impl<A: [const] Allocator + [const] Destruct> RawVecInner<A> {
     ///   initially construct `self`
     /// - `elem_layout`'s size must be a multiple of its alignment
     /// - The sum of `len` and `additional` must be greater than the current capacity
-    #[rustc_const_unstable(feature = "const_heap", issue = "79597")]
     unsafe fn grow_amortized(
         &mut self,
         len: usize,
@@ -532,7 +528,6 @@ const impl<A: [const] Allocator + [const] Destruct> RawVecInner<A> {
     // not marked inline(never) since we want optimizers to be able to observe the specifics of this
     // function, see tests/codegen-llvm/vec-reserve-extend.rs.
     #[cold]
-    #[rustc_const_unstable(feature = "const_heap", issue = "79597")]
     unsafe fn finish_grow(
         &self,
         cap: usize,

library/alloc/src/vec/mod.rs

@@ -847,6 +847,7 @@ impl<T> Vec<T> {
     }
 }
 
+#[rustc_const_unstable(feature = "const_heap", issue = "79597")]
 const impl<T, A: [const] Allocator + [const] Destruct> Vec<T, A> {
     /// Constructs a new, empty `Vec<T, A>` with at least the specified capacity
     /// with the provided allocator.
@@ -906,7 +907,6 @@ const impl<T, A: [const] Allocator + [const] Destruct> Vec<T, A> {
     #[cfg(not(no_global_oom_handling))]
     #[inline]
     #[unstable(feature = "allocator_api", issue = "32838")]
-    #[rustc_const_unstable(feature = "const_heap", issue = "79597")]
     pub fn with_capacity_in(capacity: usize, alloc: A) -> Self
     {
         Vec { buf: RawVec::with_capacity_in(capacity, alloc), len: 0 }
@@ -937,7 +937,6 @@ const impl<T, A: [const] Allocator + [const] Destruct> Vec<T, A> {
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[rustc_confusables("push_back", "put", "append")]
-    #[rustc_const_unstable(feature = "const_heap", issue = "79597")]
     pub fn push(&mut self, value: T)
     {
         let _ = self.push_mut(value);
@@ -975,7 +974,6 @@ const impl<T, A: [const] Allocator + [const] Destruct> Vec<T, A> {
     #[inline]
     #[unstable(feature = "push_mut", issue = "135974")]
     #[must_use = "if you don't need a reference to the value, use `Vec::push` instead"]
-    #[rustc_const_unstable(feature = "const_heap", issue = "79597")]
     pub fn push_mut(&mut self, value: T) -> &mut T
     {
         // Inform codegen that the length does not change across grow_one().